INCOSE Systems Engineering Handbook, 5th Edition

6 CASE STUDIES

Real-world examples that draw from diverse industries and types of systems are provided throughout this handbook, and in this part, five case studies have been selected to illustrate the diversity of systems to which Systems Engineering (SE) principles and practices can be applied: medical therapy equipment, a bridge, a breach of a cybersecurity system, a redesign of a high-tech medical system for low-tech maintenance, and autonomous vehicles. They represent examples of failed and successful systems.

6.1 CASE 1: RADIATION THERAPY—THE THERAC-25

Background Therac-25, a dual-mode medical linear accelerator (LINAC), was developed by the medical division of the Atomic Energy Commission Limited (AECL) of Canada, starting in 1976. A completely computerized system became commercially available in 1982. This new machine could be built at lower production cost, resulting in lower prices for the customers. However, a series of tragic accidents led to the recommended recall and discontinuation of the system.

The Therac-25 was a medical LINAC, or particle accelerator, capable of increasing the energy of electrically charged atomic particles. LINACs accelerate charged particles by introducing an electric field to produce particle beams (i.e., radiation), which are then focused by magnets. Medical LINACs are used to treat cancer patients by exposing malignant cells to radiation. Since malignant tissues are more sensitive than normal tissues to radiation exposure, a treatment ...